How did surgeons separate conjoined twins?

Rital and Ritag Gaboura were born joined at the head. Last week, a team of more than 15 surgeons and doctors at Great Ormond Street Hospital in London completed a series of operations to successfully separate the Sudanese twin girls. How did they do it?

Taking a closer look

The first thing surgeons do in this situation is to take a good look at the twins' skulls and brains. Magnetic resonance imaging (MRI) and X-ray computed tomography (CT) show surgeons how the skulls are fused and whether twins' brains are attached to one another. If the brains are joined, surgery is usually too risky.

The Gaboura sisters turned out to be craniopagus twins – they share a skull but not a brain. The phenomenon is rare, occurring about once in every 2.5 million births.

Next, the surgeons needed a physical 3D model of the twins' skull and brains so they could study the delicate network of arteries and veins that were transporting blood to and from their brains. In most cases, craniopagus twins do not share arteries that feed the brain, but their veins are often tangled, with some running from one twin's brain to the other's.

Carefully separating these veins is the major obstacle facing surgeons. If one twin ends up with too many veins, its heart will collapse; leave a twin with too few veins, and its brain will swell with blood.

"The sophistication is not so much in the surgical techniques," says Richard Hayward of Great Ormond Street Hospital. "It really comes down to the investigations of the blood vessels and how you make decisions about where to cut."

To model blood flow, neurosurgeons injected dyes into the twins' arteries and traced the blood's path in and out of the brain with a rapid series of X-rays. A media production company named Glassworks Amsterdam used these images to make a CGI video of blood rushing in and out of the twins' brains. The surgeons also asked Cavendish Imaging, an anatomical imaging specialist in the UK, to print a 3D model of the twins' skulls, including skin, bone and blood vessels.

A difficult separation

If craniopagus twins are in a critical condition – if one is close to heart failure, for instance – surgeons have to work as quickly as possible. However, surgeons prefer to separate craniopagus twins in stages, allowing their skulls and veins to recover between each operation. A recent review looked at the outcome of 41 craniopagus surgeries and found a death rate of 63 per cent for all-at-once operations, compared with 23 per cent for multiple-stage operations.

Although blood was not pumping evenly across the Sudanese twins' brains, meaning Ritag's heart was overwhelmed and close to failing, the surgeons decided that they had enough time to safely separate the girls in stages.

In May this year, when the twins were around 8 months old, the surgeons began to divide the veins in their brains. Two major systems of veins drain blood from the brain: a superficial system woven into outer layers of the dura mater – an envelope of protective tissue surrounding the brain – and a deep system in internal brain structures. The plan was to give one twin most of the superficial system and the other most of the deep system, in the hope that both brains would adapt to the loss by expanding small "collateral" blood vessels that connect the two systems. "If you perform the surgeries slowly enough and give time for recovery, collaterals gradually grow," explains lead surgeon David Dunaway.

For each vein-dividing surgery, the surgeons opened a window in the twins' skulls and operated on the veins in that space. When drilling through the skull to reach the blood vessels, surgeons use a craniotome – a high-speed drill equipped with a kind of "foot" that pushes the brain out of the way so that only bone is cut.

The surgeons sliced through veins, tying them off with ligatures and dissolvable sutures. When possible, shared veins were split at a junction, so that each twin got one part of the vein. The surgeons sometimes placed a sheet of non-stick material between the two brains to keep veins and tissues separate while they recovered.

The final stretch

Throughout the surgery, the surgeons were preparing for the final hurdle before full separation: craniopagus twins don't have enough bone and skin between them to form complete skulls and scalps when the time comes to sew everything up.

To solve the problem, the surgeons put four silicone balloons underneath the twins' scalps, between the bone and skin, and slowly filled them with saline solution. "The children looked very peculiar indeed with four huge lumps on their heads," says Hayward. The balloons gradually stretched the skin of the scalp so that surgeons had plenty of skin to work with during the final surgery.

Surgeons can expand bone too. Skull bone has three main layers – tough inner and outer layers separated by a spongy middle. By driving chisels between them, surgeons can split the bone, lift up a section and so double its original area. In young children, the dura can regenerate bone, Dunaway says. Rital and Ritag will probably need further surgery to fully repair their patchworked skulls.

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